The present invention relates generally to manhole assemblies and more particularly to adjustment risers for a manhole frame, a catch basin frame or the like.
A manhole is a structure which provides a passageway into an underground system (e.g., an underground drainage, sewage, electrical, telephone or cable system). In this manner, a manhole (also commonly referred to in the art as a maintenance hole) enables a worker to descend into the underground system for the purpose of performing routine maintenance and/or servicing, which is highly desirable.
A manhole typically enables one to descend down into an underground system from a paved surface, such as a street. Referring now to FIG. 1, there is shown an exploded view of a manhole assembly 10 that extends from a paved surface (not shown) down into an underground system (not shown). Specifically, assembly 10 includes an elongated pre-cast manhole 11, manhole 11 extending vertically up from an underground system to a location spaced adequately beneath the paved surface. Manhole 11 is shaped to include a central opening 13 which is sized and shaped to enable a worker to pass therethrough. Commonly, one or more steps and/or handles are affixed onto the inner surface of manhole 11 to help the worker to travel through central opening 13.
One or more annular concrete risers 15 are stacked directly on top of pre-cast manhole 11, the lowermost riser 15-1 being affixed to the top surface of manhole 11 by a layer of sealant, such as tar or any other conventional caulking material, to limit water infiltration. The central hole in each riser 15 is preferably axially aligned with the central opening 13 in manhole 11 so as to create a continuous passageway through which a worker can pass. Each riser 15 (also commonly referred to in the art as an adjustment riser) is typically constructed of a concrete material so as to render it less susceptible to cracking and/or salt damage.
Furthermore, a manhole frame 17 is disposed directly above the uppermost riser 15-2. The manhole frame 17 is typically constructed of a rigid and durable material, such as cast-iron, and includes a flat annular platform 19 and an annular ring 21 which extends orthogonally up from platform 19. The annular ring 21 is commonly provided with an inwardly protruding flange 23 which is sized and shaped to support a disc-shaped manhole cover 25. Preferably, manhole cover 25 is sized and shaped to fit snugly within the opening defined by ring 21, with the top surface of manhole cover 25 lying flush with the top surface of ring 21. In this manner, it is to be understood that manhole cover 25 serves as a means for enclosing the passageway into the underground system at the street level, thereby rendering the street safe for traffic when access to the underground system is not required.
Ideally, the top surface of the manhole frame 17 (and similarly the manhole cover 25) lies substantially flush with the paved surface. Failure to position the top surface of manhole frame 17 flush with the paved surface can cause considerable cracking and/or pitting between frame 17 and the paved surface over time (i.e., due to stress and vibratory forces created from traffic traveling on the paved surface). As can be appreciated, cracking and/or pitting of the paved surface immediately surrounding frame 17 can lead to excessive water infiltration into the underground system and/or the formation of substantial potholes in the paved surface, both of which are highly undesirable.
Accordingly, an intermediate layer of material (not shown) is typically provided between the uppermost riser 15-2 and the underside of platform 19 of manhole frame 17 to ensure that the top surface of manhole frame 17 (as well as manhole cover 23) lies substantially flush with the paved surface. This intermediate layer is often constructed using either concrete or the combination of brick and mortar.
It should be noted that town, city and/or state construction ordinances often mandate that the distance D between the top surface of manhole 11 and the top surface of frame 17 (i.e., the surface of the roadway) be a specified minimum value (e.g., 12 inches) to allow for future work on the roadway (e.g., repaving the surface) without damaging the manhole 11. Specifically, in order to repave a roadway, considerable pulverization of the paved surface is typically required. As such, prior to the pulverization of the paved surface, workers are required to break away the intermediate layer and, in turn, remove the risers 15 and frame 17. Once the risers 15 and frame 17 have been removed, the pavement is typically pulverized down to the top surface of the manhole 11.
The aforementioned intermediate layer is typically formed between the uppermost riser 15-2 and the manhole frame 17 in the following manner. Specifically, after the one or more risers 15 have been positioned on top of the manhole 11 (using a crane or other similar machine) and sealed thereto, the intermediate layer is then deposited on top of the uppermost riser 15-2, the particular height of said intermediate layer being calculated so that the top surface of manhole frame 17 will lie flush with the paved surface. Before said intermediate layer has an opportunity to fully cure (i.e., harden), frame 17 is deposited thereon. Accordingly, once said intermediate layer cures, frame 17 is effectively secured onto uppermost riser 15-2 in a manner which prevents the infiltration of water into the underground system.
It has been found that the use of such an intermediate layer of material between the uppermost riser and the manhole frame introduces a number of notable drawbacks.
As a first drawback, it has been found that the considerable weight of the manhole frame often compresses the intermediate layer before it has an opportunity to cure. As a result, the top surface of the manhole frame often fails to lie flush with the paved surface, which is highly undesirable for the reasons noted in detail above.
As a second drawback, the aforementioned method of depositing said intermediate layer of material between the uppermost riser and the manhole frame has been found to be inadequate when the paved surface is not flat. In particular, paved surfaces are often crowned in the lateral direction (i.e., bowed such that its center is raised slightly higher than along its sides) to promote proper drainage. As a result, the frame is often shimmed at an angle relative to the uppermost riser (so as to be flush with the bowed pavement around its entire periphery) using construction remnants, shards of concrete and/or other debris. However, it has been found that the inaccurate nature of such a shimming technique can cause deterioration (i.e., cracking and pitting) in the paved surface around the frame, which is highly undesirable for the reasons noted in detail above.
As a third drawback, the utilization of products in said intermediate layer which require a significant curing period (e.g., concrete, mortar, etc.) necessitates that the deposition of said layer be undertaken only during ideal weather conditions, which is highly undesirable.
As a fourth drawback, said intermediate layer is typically constructed out of a material which is not reusable. Accordingly, when road construction is performed which necessitates the separation and removal of the frame and risers from the manhole, subsequent reconstruction of the manhole with its complementary parts necessitates the complete reconstruction of the intermediate layer, which is highly undesirable.
Accordingly, rubber (or rubber composite) adjustment risers are well known in the art and are commonly used as a means to orientate the top surface of a manhole frame flush with the paved surface. Rubber adjustment risers are commonly constructed as thin, unitary rings which are relatively fixed in shape (an example of a rubber composite adjustment riser being shown in U.S. Pat. No. 5,723,192 to S. Jonasz, which is incorporated herein by reference). In use, one or more rubber adjustment risers are stacked between the uppermost riser and the manhole frame so as to render the top surface of the frame flush with the paved surface, the rubber construction of said risers serving as a gasket for limiting water infiltration. It should be noted that rubber adjustment risers of the type described above are often constructed either: (1) with substantially flat and parallel top and bottom surfaces or (2) with a substantially flat bottom surface and with an angled, or tapered, top surface so as to provide the riser with a wedge-like construction for use with paved surfaces which are not flat.
Although well-known in the art, rubber adjustment risers of the type described above suffer from a few notable drawbacks.
As a first drawback, rubber adjustment risers of the type described above are relatively fixed in shape. Because a paved surface frequently has a unique contour, the pre-formed shape of an rubber adjustment riser often fails to precisely align the top surface of the manhole frame flush with the pavement, which is highly undesirable. Furthermore, the large variety of differently sized and shaped rubber adjustment risers increases the storage requirements of its user, which is highly undesirable.
As a second drawback, a rubber adjustment riser of the type described above has a certain level of compressibility. Due to its compressibility, it has been found that the rubber adjustment riser often acts as a shock absorber for traffic passing on the paved surface which, in turn, eventually disturbs the pavement area immediately surrounding the manhole frame, which is highly undesirable.
As a third drawback, it has been found that rubber adjustment risers of the type described above are not as effective in preventing the infiltration of water into the underground system as concrete or the combination of brick and mortar, which is highly undesirable.
As a fourth drawback, it has been found that rubber adjustment risers of the type described above are not considerably durable. Rather, rubber adjustment risers have been found to be susceptible to deformation and/or breakage when subjected to the vibratory forces produced from strenuous road conditions, which is highly undesirable.